Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Goodwill by Reporting Segment (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2014	Mar. 31, 2015	Aug. 01, 2012	Jun. 30, 2014	Sep. 30, 2014	Mar. 31, 2013
Goodwill [Roll Forward]
Goodwill, ending balance	$ 276,097us-gaap_Goodwill	$ 571,271us-gaap_Goodwill
SMSC Acquisition [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance			165,592
Goodwill, ending balance			165,592
Supertex Inc. [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance				133,713
Goodwill, ending balance		143,160		133,713
ISSC Technologies Corporation [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance					152,243
Goodwill, ending balance		154,399			152,243
Semiconductor products [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance						252,148
Goodwill, ending balance	256,897	552,071				252,148
Semiconductor products [Member] \| SMSC Acquisition [Member]
Goodwill [Roll Forward]
Purchase accounting adjustments	(3,473)
Semiconductor products [Member] \| Other business acquisitions [Member]
Goodwill [Roll Forward]
Additions due to business combination	8,111	624
Semiconductor products [Member] \| Acquisition of R and E International Member
Goodwill [Roll Forward]
Additions due to business combination	111
Semiconductor products [Member] \| Supertex Inc. [Member]
Goodwill [Roll Forward]
Additions due to business combination		143,160
Semiconductor products [Member] \| ISSC Technologies Corporation [Member]
Goodwill [Roll Forward]
Additions due to business combination		154,399
Foreign currency translation adjustments		(3,009)
Technology licensing [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance						19,200
Goodwill, ending balance	19,200	19,200				19,200
Technology licensing [Member] \| SMSC Acquisition [Member]
Goodwill [Roll Forward]
Purchase accounting adjustments	0
Technology licensing [Member] \| Other business acquisitions [Member]
Goodwill [Roll Forward]
Additions due to business combination	0	0
Technology licensing [Member] \| Acquisition of R and E International Member
Goodwill [Roll Forward]
Additions due to business combination	0
Technology licensing [Member] \| Supertex Inc. [Member]
Goodwill [Roll Forward]
Additions due to business combination		0
Technology licensing [Member] \| ISSC Technologies Corporation [Member]
Goodwill [Roll Forward]
Additions due to business combination		0
Foreign currency translation adjustments		$ 0